If you're after free software then for 2.5D machining and engraving then CAMbam free edition is pretty good. You'll be able to import drawings from most programs into it since it accepts .dxf format.
For more complicated 3D parts your options are more limited, CNC Toolkit is one which can do just about anything (3D models, V-carving etc) but isn't the easiest to use.

To control the machine LinuxCNC is excellent and contrary to popular belief, is no longer hard to configure. If you need help with any of these programs just ask...